Method for preparing anodes for cathodic protection systems



United States Patent 2,998,359 METHOD FOR PREPARING AN ODES FOR CATHODICPROTECTION SYSTEMS Edward P. Anderson, Livingston, N.J., assignor, bymesne assignments, to Engelhard Industries, The, Newark,

NJ., a corporation of Delaware No Drawing. Filed Nov. '25, 1958,,Ser.No. 776,206

This invention relates to the preparation of anodes for cathodicprotection purposes. 7

For the protection of the painted surfaces of a ship againsh corrosion,it has been proposed to employ electrodes insulated from the ships hull,and to apply a potential between the electrodes and the hull. The flowof current to the painted surface has the -e'ffectjof greatly reducingrusting and corrosion.

The construction of anodes for this type of system presents manyproblems. In this regard it has been proposed heretofore to use atitanium or tantalum base clad with platinum. The relatively thick layerof expensive platinum which is employed and the expensive claddingprocess make this method relatively costly.

Accordingly, a principal object of the present invention is to reducethe cost of making anodes for cathodic protection systems.

In accordance with the present invention this object is achieved byusing a spray coating technique for applying platinum to titanium ortantalum. Following the spray coating, the platinum may be distributedby a burnishing operation. The anode is then immersed in an electrolytesuch as sea water and current is passed between the anode and thesurface to be protected. This has the effect of oxidizing any surfaceareas of the tantalum or titanium base which are not covered withplatinum. The resultant platinum-spattered anode with spaced oxideregions on its surface maintains its form and is not subject tocorrosion when used in cathodic protection systems.

The process as described above has the significant advantage of beingmuch less expensive than the elaborate process required for the completecladding of a titanium or tantalum base with platinum.

Other objects, advantages and various features of the invention will beapparent from the following detailed description.

As mentioned briefly above, the present lnventlon basically involves thesteps of spraying platinum on a base of tantalum or titanium, immersingthe electrode in an electrolyte and drawing current from the electrode.In this process, preliminary steps for preparing the titanium ortantalum surface for spraying, and a burnishing step following the spraycoating may advantageously be employed.

In the preparation of a surface for receiving a spray coating,subsidiary steps may be taken. Thus in the present case, the base oftitanium or tantalum may be given a flash electroplating of platinumprior to the spray by molten droplets of platinum. The surface may alsobe roughened mechanically to some extent so that the subsequent spraycoating of platinum will more readily adhere to the titanium or tantalumbase. Sandblasting can be used as the roughening technique. The processof spraying molten platinum also serves to raise the temperature of thebase. This heating facilitates the bonding of the platinum layer to thebase.

The spraying operation may be accomplished through the use of acommercially available metalizing gun. In view of the relatively highmelting point of platinum, a metalizing gun employing an oxy-acetylenecombustion flame may advantageously be employed. In passing, it

may be noted that a suitable metalizing gun is shown as part of theapparatus in James S. Hill application Serial No. 765,101, filed October3, 1958.

Following the spraying operation, the covering of the titanium ortantalum base may be improved by a burnishing operation. Burnishinginvolves a plastic smearing such as may occur on metallic surfacesduring buffing operations. In the present case, burnishing of theplatinu'm material may be accomplished by subjecting the sprayed surfaceto the rubbing rotary action of a burnishing tool held, for example, inthe chuck of a lathe. In one instance, a hardened tool steel burnishingtool was successfully employed. In addition, rolling or other similarmechanicaloperations may be employed to spread the platinum. When thespraying operation provides a sufficiently flat and uniform coating ofplatinum over the "greater portion of the sprayed surface of the base,however, the burnishing operation need not be employed.

Depending on the type of anode which is being constructed, the formationof a complete anode assembly may take place prior to or subsequent tothe spraying and burnishing operations discussed above. Thus, forexample, when the metal portion of the anode is in the form of sheetmetal stock, the spraying and burnishing operations would normallyprecede assembly with the plastic support for the anode. In cases inwhich the titanium or tantalum base must undergo substantial machiningoperations, however, these operations are normally perfonned prior tothe spraying and burnishing steps. Two representative patentapplications disclosing anodes of these two types for cathodicprotection systems are E. P. Anderson, application Serial No. 754,778,filed August 13, 1958, and A. I. Zwanzig, application Serial No.682,336, filed September 6, 1957.

The anode assembly including the platinum coated titanium or tantalumbase is then secured to the hull of a ship or otherwise mounted adjacentthe painted structure which is to be protected. Current at the properlevel is then applied between the anode and the surface requiringprotection against corrosion. The spraying proc ess will normally leavecertain areas of the titanium or tantalum material which are not coveredby a platinum coating. Immersion of the anode in water, and theapplication of current between the anode and the surface to be protectedproduces a chemical reaction on the bare portions of the titanium ortantalum base. This reaction, possibly resulting from electrolyticdecomposition, in itially produced at the surface of the titanium ortantalum material, produces an insulating oxide which covers these baresurfaces of the base material. Thereafter, current flows from the anodesurface only through the platinum surface coating. In view of theprotection of the base material by the oxide layer, however, the anodeassembly as a whole retains its original form and is not subject tocorrosion.

Although platinum is preferred for the surface coating, it is to benoted that a noble metal coating, including a significant proportion ofplatinum, may also be used. In this regard, an alloy of palladium andplatinum may be employed for the preparation of the anode surfaces forcathodic protection systems.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. A method for the preparation of anodes for cathodic protectionsystems comprising the steps of flash electroplating a base of amaterial selected from the group consisting of titanium and tantalumwith platinum, roughening the plated surface of the base, spraying thebase with additional platinum to form a discontinuous coating,burnishing the sprayed surface to form an electrode, immersing theelectrode in an electrolyte, and applying a voltage between theelectrode connected as an anode and the electrolyte whereby an oxidelayer is formed on those portions of the base not completely coated byplatinum.

2. A method comprising the steps of flash plating with platinum a basemade of a material selected from the group consisting of tantalum andtitanium, spraying the base with additional molten platinum to form adiscontinuous coating, burnishing the resulting surface, immersing theplatinum-coated base in an electrolyte, and applying a voltage to thecoated base connected as an anode, whereby an oxide layer is formed onportions of the base not fully coated by platinum.

3. A method of preparing anodes for cathodic protection systemscomprising the steps of spraying platinum on a base made of a materialselected from the class consisting of tantalum and titanium to form adiscontinuous coating, burnishing the resulting surface, immersing theplatinum-coated base in an electrolyte, and applying a voltage to thecoated base connected as an anode whereby an oxide layer is formed onthose portions of the base not completely coated by platinum.

References Cited in the file of this patent UNITED STATES PATENTS1,077,920 Stevens Nov. 4, 1913 1,477,099 Baum Dec. 11, 1923 2,282,022Bishop et al. May 5, 1942 2,719,797 Rosenblatt et a1. Oct. 4, 19552,719,820 Allen Oct. 4, 1955 2,915,406 Rhoda Dec. 1, 1959 OTHERREFERENCES Cotton: Platinum-Faced Titanium for Electrochemical Anodes,Platinum Metals Review, vol. 2, No. 2,

20 April 1958, pp. 45-47.

1. A METHOD FOR THE PREPARATION OF ANODES FOR CATHODIC PROTECTIONSYSTEMS COMPRISING THE STEPS OF FLASH ELECTROPLATING A BASE OF AMATERIAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND TANTALUMWITH PLATINUM, ROUGHENING THE PLATED SURFACE OF THE BASE, SPRAYING THEBASE WITH ADDITIONAL PLATINUM TO FORM A DISCONTINUOUS COATING,BURNISHING THE SPRAYED SURFACE TO FORM AN ELECTRODE, IMMERSING THEELECTRODE IN AN ELECTROLYTE, AND APPLYING A VOLTAGE BETWEEN THEELECTRODE CONNECTED AS AN ANODE AND THE ELECTROLYTE WHEREBY AN OXIDELAYER IS FORMED ON THOSE PORTIONS OF THE BASE NOT COMPLETELY COATED BYPLATINUM.